Direct access storage devices (DASD) have become part of every day life, and as such, expectations and demands continually increase for better performance at lower cost. To meet these demands, the mechano-electrical assembly in a DASD device, specifically the Hard Disk Drive (HDD) has evolved to meet these demands.
In order for an HDD to hold more data, advances in the magnetic transducer as well as the disk media on which the data is written have undergone major advances in the past few years. A critical relationship between the head and disk is the spacing between their adjacent surfaces. This is typically known as the fly height.
The magnetic transducer flies above the disk by virtue of an air film created by the disk spinning next to a pattern on the surface of the slider (and magnetic transducer contained there within). This pattern on the slider is known as the Air Bearing Surface, or ABS. The ABS is fabricated on the surface of the slider that is closest to the disk. Typically the closest point on the ABS to the adjacent disk surface resides on the magnetic transducer. Typically the magnetic transducer resides at the end of the slider known as the trailing edge of the slider, so called the trailing edge because it is the last edge of the slider to fly over the disk.
Control of the fly height is critical to the density of data that can be written onto the disk surface. Of similar importance to the density of data that can be written onto the disk surface is the geometry of features inside the magnetic transducer. The feature that is critical for the write function of the magnetic transducer is known as throat height. The feature that is critical for the read function of the magnetic transducer is known as stripe height. Both stripe height and throat height are controlled by a lapping process, which establishes the initial surface on the slider for defining the ABS. The lapping process simultaneously defines the initial surface of the ABS, stripe height, and throat height.
Initially, a slider starts as a small part of a much larger wafer containing tens of thousands of potential sliders, deposited on the wafer in an array of rows and columns. A section of the wafer is cut from the wafer for processing. This section is known as a quadrant or quad. A quad typically contains several non-parted rows. Typically a row of sliders is lapped before the row is parted from the quad. The success of the lapping process for simultaneously defining the ABS, stripe height, and throat height is predicated on the quad having a sliced surface that is flat and parallel to the features inside the magnetic transducer that define stripe height and throat height.
The alignment of the features inside the magnetic transducer to each other and to the wafer, which define stripe height and throat height, are typically very precise due to the photolithographic processes that define the features' geometry and location. However, this precise alignment and location can be disturbed by stress internal to the wafer.
Internal stresses inside a wafer are in balance prior to being sliced. Once a part of a wafer (such as a row or a quad of rows) is removed, the internal stresses will typically rebalance themselves and typically distort the wafer, row, and/or quad in the process of rebalancing stresses. This distortion disturbs the alignment of the features to each other inside the magnetic transducer that define stripe height and throat height.
The problem arises as to how to mitigate this stress-induced distortion and maintain alignment of the features inside the magnetic transducer that define stripe height and throat height. Since millions of dollars are invested in current tooling, mitigation of this stress-induced distortion must have minimal impact on the existing set of tools as well as minimal impact on the fabrication process and wafer.